Means anchoring tensioned cable for prestressed concrete



E. FREYSSINET Nov. 1s, `195.2

MEANS ANCHORING TENSIONED CABLE FOR PRESTRESSED CONCRETE Filed June 8,1945 .'q Qq .ZNvc/vrol? La uw Cu., Mmm..

Patented Nov. 18, 1952 UNITED STATES il f TENT OFFICE Eugne Freyssinet,Neuilly-sur-Seine, France Application June 8, 1945, Serial No. 598,313In France September 30, 1941 Section 1, Public Law 690, August 8, 1946Patent expires September 30, 1961 Claims.

In my prior U. S. Patent No. 2,270,240, I have described means foranchoring tensioned cables passing through concrete masses to which theydo not adhere. The cable to be anchored is passed through a Very strongtube embedded in concrete and strongly adherent thereto, then the cableis tensioned by extraneous means, and a soft substance capable ofhardening, such as cement mortar, is compressed very tightly between thecable component wires and the inner wall of the tube; in the case wherethe tube provides a generally frusto-conical or aring recess,compression is obtained for instance by means of a wedge forced into therecess along the axis thereof. The purpose of cement mortar was toprovide for an even action on the various wires in spite of fortuitousdiameter dilferences; however, I have found that the mortar is notaltogether necessary to serve the purpose aimed at.

It is an object of my invention to provide improvements in ormodifications of my aforesaid anchoring means.

Instead of being lined by a steel tube as disclosed in my aforesaidpatent, the wall of the frusto-conical or flaring recess in concrete maymerely be lined with a hoop of hard steel having a high tensilestrength, the hoop being made of contacting coils. The conical wedgeforced along the recess axis may be a mass of concrete provided with anouter hard steel hoop or steel sheet; such outer coatings providing forregularization or even distribution of compressional forces from thewires on concrete in the wall of the recess and the wall of the wedge soas to prevent damage to said concrete but they allow an amount ofplastic deformation of the combination of parts, which secures an evenaction on the various Wires as a hydraulic distribution would do.

It is possible to manufacture a separate anchorage unit or block made ofconcrete having a frusto-conical recess lined with a hoop embedded insaid concrete and a second hoop of soft steel proximate to the peripheryof the concrete mass; the blocks may be positioned at proper location inthe planking when the cables are placed before pouring concrete.

The following description with reference to the appended drawings givensolely by way of example will show how this invention may be carriedout.

Fig. 1 is an axial section taken along the axis of a cable and showingan anchoring device in accordance with my invention.

Fig. 2 is a diagrammatic development drawn on a smaller scale, of a hoopdisposed around the anchorage block.

Fig. 3 is a longitudinal section of a wedge.

Fig. 4 is a cross section of a modified wedge.

Referring to Fig. 1, the reference character l designates cable wiresaccommodated in a sheath 2 positioned before pouring concrete 3, asdisclosed in my prior patent. At either end of the cable or, at one endthereof should the other end be provided with usual anchoring means, ananchoring unit or block manufactured beforehand, and to be presentlydescribed is secured. The block includes a substantially cylindricalmass 4 of high grade concrete having a soft steel hoop 5 near itsperiphery, and a substantially frustoconical recess 6 along the axis ofthe cable to be tensioned, through which the cable wires pass. The innerwall of the recess is lined with a hoop 'I consisting of contactingcoils of hard steel having a high tensile strength, around whichconcrete ll is poured. The block thus constituted is threaded on thecable end before pouring concrete 3 and secured to the planking. Aroundthe block is disposed a hoop connsistingI of a wire 8 which is festoonedin zig-zag fashion, and a few coils 9 as shown in development on asmaller scale on Fig. 2.

Concrete 3 is then poured. When said concrete has set and hardened, theplanking is taken away and a wedge I0 is forced into the recess alongits axis; the wedge I0 (Fig. 3) may be made of high strength concrete IIcast into the annular space between a central tubular steel core I 2 anda frusto-conical hoop I3 having contacting coils of hard steel. By meansof a, jack device as described in my prior patent, the outer ends Ia ofwires I are drawn to be tensioned as required, after which the wedge I0is driven into the recess so as to squeeze the cable wires between thewedge and the recess wall.

Owing to the squeezing action, hoop I is subjected to a high stresscausing a resilient deformation thereof, and concrete 4 of the anchoringblock is compressed between said hoop 'I and hoop 5 which is alsostressed although to a less degree. Hoop 8, 9 acts to distribute throughconcrete 3, the forces transferred to the outer hoop 5 of the anchoringblock.

Anchoring is thus performed; the jack device may be removed and the endsIa of wires I cut away.

Through the central core I2 in Wedge I0, a rustproong material may beinjected into sheath 2 for instance cement, synthetic resin or any otherlling. material.

In the modied wedge shown on Fig. 4, a steel sheet I4 is substituted forhoop I3; sheet I4 may be provided with corrugations Ida located alonggenerating lines of the cone, for accommodation of the cable Wires.

The plasticity of the outer conical Wall and of the wires (of the cable)themselves are sufficient -to provide for anchorage of all Wires inspite of any small difference in diameter thatY they may p exhibit.

An advantage of my process is that the Wires can be tensioned by degreesor steps; after ar first tensioning, the jack may be mounted again, thewires drawn, the Wedge removed and then reset after increasing ordecreasing tension. In the latter case, it is only necessary to hold theWedge apart from its nal position by any suitable device. f

While I have described; What I deem to be an elcient and reliableembodiment of my invention, I do not Wish to be limited thereto as manyalterations may be brought therein without departing from the spirit ofthe appended claims.

What I claim is:

l. In combination With an open-centered bundle ofV stretchedA steelWires, a pair of cooperating gripping units for maintaining said wiresin stretched condition, which comprises an annular concrete structurethrough which said wires extend, having a daring, inner, Wire-contactingWall providing a backing for said wires, said inner, wire-contactingWall being faced with mutually contacting coils of Wire, and a aringwedge having an outer peripheral surfaceA of mutually contacting coilsof. wire providing a Wire-contacting Wall, said wedge being held incompressed condition within said bundle to nip said steel wires betweensaid Wire-contacting walls and having its outer surface conformed to thegeneral shape of the inner surface of said Wire bundle, at least one ofsaid uni-tsy comprising a plasticallyV deformable concrete portion inring formation adjacent said Wire-contacting wall thereof.

2. The structure of claim 1, said Wedge having a core of plasticallydeformable concrete confined REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES' PATENTS Number Name Date 453,286 Lieb June 2, 18912,173,698 Schenk Sept. 19, 1939- 2,264,035 Birkhofe-r Nov. 25,19412,270,240 Freyssinet Jan. 20, 1942 FOREIGN PATENTS Number Country Date5451,43? Great' Britain Nov.Y 26, 1941

